Optical packet switching is considered a key technology in the development of optical communication networks. Fast tunable lasers can be used to color bursts of data according to their destination. A tuning time as fast as the order of a nanosecond enables the implementation of efficient burst switching, as described in the article “Optical switching speed requirements for Terabit/sec packet over WDM networks” by D. Sadot, and I. Elhanany, published in IEEE Photonics Technology Letters, Vol. 12, no., 4, pp. 440-442, April 2000. The accurate measurement of wavelength transients increases the efficiency of optical burst switching, by making it possible to ascertain mode stability in the minimum possible time.
A number of different types of tunable lasers which offer the combination of wide tuning range and fast tuning are in common use, such as DBR, SG-DBR, GCSR, and DS-DBR lasers. Such lasers have been implemented in a number of different systems described in various publications.
Prior art methods of measuring spectral wavelength transients are often based on the accuracy of an optical wavelength selective element. By applying a step function signal to drive the laser's tuning section(s) and filtering the resulting optical signal through the wavelength selective device, the wavelength transients can be measured. One such experimental method has been described in the article entitled “Measurements of thermal frequency chirp in directly modulated DFB lasers and thermal transient induced frequency drift during fast tuning in GCSR lasers using frequency discrimination technique,” by E. Buimovich and D. Sadot, published in the Proceedings of LEOS Annual Meeting, Paper TuD7, vol. 1, pp. 208-209, Tucson, Ariz. 2003, in which there is described an apparatus for performing this method, as shown in FIG. 1. The time resolved frequency evolution of the laser is obtained by f(t)=H−1 (A(t)/B(t)), where H represents the response of the wavelength selective device as a function of wavelength, and B(t) and A(t) are respectively the time dependent response functions of the laser output resulting from the step input function, and of the laser output resulting from the step input function modified by transmission through the wavelength selective device.
One disadvantage of such time-resolved wavelength measurement methods is that they are limited in spectral resolution by the resolution of the wavelength selective devices, which is generally significantly less than that of electronic filtering and measuring techniques. There therefore exists a need for a method of performing on tunable lasers, high resolution spectral measurements having the accuracy and resolution of electronic filtering techniques.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are incorporated herein by reference, each in its entirety.